This invention relates to a method, system and product for audiophile quality subband encoding of digital data representing audible signals.
To more efficiently transmit digital audio data on low bandwidth data networks, or to store larger amounts of digital audio data in a small data space, various data compression or encoding systems and techniques have been developed. Many such encoded audio systems use as a main element in data reduction the concept of not transmitting, or otherwise not storing, portions of the audio that might not be perceived by an end user. As a result, such systems are referred to as perceptually encoded or xe2x80x9clossyxe2x80x9d audio systems, since a portion of the data is eliminated (i.e., xe2x80x9clostxe2x80x9d) based on the expected perception of the end user.
However, some end users can perceive this data loss. Perceptually encoded audio systems are therefore not considered xe2x80x9caudiophilexe2x80x9d quality. In that regard, for an end user that can detect this data loss; the intermittent nature of data being transmitted in some audio frames and not transmitted in other frames causes an odd type of distortion.
Moreover, processing of lossy perceptually encoded audio data is limited. For example, if the data at a specific frequency needs to be boosted in level, but that data has been eliminated by the encoding process, such data processing cannot be accomplished
The dynamic range of most perceptually encoded audio systems is in the 120 dB range, quantized in 2 dB steps. While this represents an improvement over conventional compact discs, which have a dynamic range slightly wider than 90 dB, compact discs are closer to audiophile quality than perceptually encoded audio systems.
Compact discs, however, suffer from the added limitation that the distortion of audio at low levels is quite high. In that regard, low level signals on a standard 16 bit resolution compact disc, such as 70 dB below maximum, have distortion on the order of 20%. By comparison, normal compact disc distortion is approximately 0.001% at maximum level. However, maximum level cannot be used efficiently on a compact disc. Because of the nature of sound, only peaks occupy the top 10 dB maximum region, and peaks need not be low in distortion. As a result, most audiophiles desire an audio system with more than 16 bits of resolution to avoid such low level distortion.
Thus, there exists a need for an improved method, system and product for encoding a digital signal representing an audible sound. Such a method, system and product would encode digital audio signals in a fashion, such that the signals are provided with an audiophile quality. Moreover, such a method, system and product would also encode digital audio signals with a very large dynamic range.
Accordingly, it is the principle object of the present invention to provide an improved system and method for encoding a digital signal representing an audible sound.
According to the present invention, then, a method is provided for encoding a digital signal representing an audible sound. The method comprises dividing the digital signal into a plurality of frames, dividing each of the plurality of frames into a plurality of subbands, and assigning each of the plurality of subbands an indicator selected from the group consisting of positive, zero, and negative, wherein the indicator selected is based on a polarity and a magnitude of the subband. The method further comprises assigning each of the plurality of subbands one of a plurality of scale factor steps, wherein each scale factor step represents a sound level range of at most two decibels, and generating a digital word for each of the plurality of frames, each digital word having a scale factor section including the scale factor steps for the plurality of subbands in the frame, and a sample data section including the indicators for the plurality of subbands in the frame.
A system for encoding a digital signal representing an audible sound is also provided. The system of the present invention comprises a sampler for dividing the digital signal into a plurality of frames, and a filter for dividing each of the plurality of frames into a plurality of subbands. The system further comprises control logic operative to assign each of the plurality of subbands an indicator selected from the group consisting of positive, zero, and negative, wherein the indicator selected is based on a polarity and a magnitude of the subband, assign each of the plurality of subbands one of a plurality of scale factor steps, wherein each scale factor step represents a sound level range of at most two decibels, and generate a digital word for each of the plurality of frames, each digital word having a scale factor section including the scale factor steps for the plurality of subbands in the frame, and a sample data section including the indicators for the plurality of subbands in the frame.
A product for encoding a digital signal representing an audible sound is also provided The product comprises a storage medium having computer readable programmed instructions recorded thereon. The instructions are operative to assign each of a plurality of subbands in each of a plurality of frames of the digital audio signal an indicator selected from the group consisting of positive, zero, and negative, wherein the indicator selected is based on a polarity and a magnitude of the subband, assign each of the plurality of subbands one of a plurality of scale factor steps, wherein each scale factor step represents a sound level range of at most two decibels, and generate a digital word for each of the plurality of frames, each digital word having a scale factor section including the scale factor steps for the plurality of subbands in the frame; and a sample data section including the indicators for the plurality of subbands in the frame.
Still further an alternative method for encoding a digital signal representing an audible sound is also provided. The method comprises dividing the digital signal into a plurality of frames, dividing each of the plurality of frames into a plurality of subbands, and assigning each of the plurality of subbands an indicator representing frequency and phase information The method further comprises assigning each of the plurality of subbands one of a plurality of scale factor steps, wherein each scale factor step represents a sound level range of at most two decibels, and generating a digital word for each of the plurality of frames, each digital word having a scale factor section including the scale factor steps for the plurality of subbands in the frame, and a sample data section including the indicators for the plurality of subbands in the frame.
These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings.